Thank you, everyone, for your perspectives.
Tez3, thank you also for the links.
It would be ludicrous and bulky to try and respond to each of you individually, since so many posts have been written since I last had time to respond, so I am just going to respond generically.
Regarding the treatment of students and its effect on boosting self-esteem and confidence, many of the ways listed/linked to for making a child feel valued and respected are things I am already careful to do with my students. I will admit that I can become caught up in the need to get X, Y, and Z done before the end of class and give quick, general praise as a result, rather than targeted, specific praise, but it is something I am working on.
Sadly, it will take a while of my support to undo the damage done by the previous instructor. I am thinking of asking the dad if there were any incidents when Johnny came home taking about comments the instructor made to him, so I can know better the damage I'm dealing with.
Regarding sparring, I am going to try to get him back into going to class. I know the dad will support this, but it will be difficult to convince Johnny. I'm looking at pairing him with hand-picked partners who I know will use control and not steamroll him. I'm also wondering if pre-teaching the drills that will be taught at sparring that week would help him be more confident. We can't do any contact sparring in regular classes, due to a lack of gear, etc., plus I'm not so sure I can trust that class to stick to no contact to light contact sparring.
I'm also going to pull out our body shield and either I or my assistant instructor will hold it so they can practice kicking against resistance. Actually, once everyone is used to the concept of the shield, I can have them hold it for each other, and that will deal with the issue of not being able to do contact sparring in class.
I appreciated the idea of the "stand your ground" drills. I think those will be very useful, and not just for Johnny. We do something sort of similar with a pool noodle, but there's a big difference in brain response between seeing a noodle coming and seeing a fist coming.
In our adult classes, every once in a while we have a class that I call "realistic self defense day." Basically, we work in groups of 4+, and everyone takes a turn being the victim. The other students in the group grab the "victim" any way they like, as hard and realistically as they can, and the "victim" has to either subdue the attacker or get away. It's basically no holds barred self defense practice. It's a blast, and I know it's made me more confident in my own ability to defend myself. I would love to do this with Johnny and his class, but I feel like I'd end up with a class full of kids upset at each other. We adults are proud of the bruises we get (and inflict!) doing this drill...the kids, not so much.
Now to get all this done while still getting everyone ready for their next belt test.